Numerous different filter materials and material combinations are used for vacuum-cleaner bags. In addition to the conventional paper or paper-tissue bags, bags which are made of combinations of paper with synthetic non-woven or even vacuum-cleaner bags which consist completely of non-wovens are known. Thus for example the document EP-A-0 338 479 describes a paper/meltblown combination and the document EP 0 161 790 describes a triple-ply spunbond/meltbond/spunbond composite (SMS). Such filter materials which have a fine-filter layer formed from meltblown material considerably improve the deposition efficiency compared with a single-ply paper bag or a double-ply paper-tissue bag. In recent years, multilayer composite materials of differing composition have in addition increasingly become known by means of which especially the dust storage capacity has been able to be improved. In EP-A-0 960 645 is described a material of this type formed from different non-woven layers and a fine-filter layer.
The use of these novel composite materials for manufacturing vacuum-cleaner bags has led to the possibility of extending the service life of said bags.
However, the extension of the service life which can be achieved using these novel filter bags is still in need of improvement in the sense of optimal exploitation of the filter bag especially when the filter is highly loaded with fine dust. Furthermore it is desirable also to considerably extend the service life of filters which are made of simple combined filter media.
Furthermore, from DE-0S 27 33 861 A is known a filter arrangement for a vacuum-cleaner. In the filter arrangement described there, a surface-active material is contained in a receptacle which consists of a dimensionally stable material and is delimited by two sieve-plates. This filter arrangement is therefore also used in accordance with the teaching of the disclosure document as a pre-filter for a vacuum-cleaner, i.e. the arrangement formed from a dimensionally stable material is positioned upstream of the actual vacuum-cleaner bag.
A substantial disadvantage of this arrangement, however, is that this device is only suitable for filtering out any fine dust which might occur. In the event of other dust fractions being present as well as the fine dust, this filter arrangement cannot be used since in these cases the sieve-plates delimiting the receptacle would become clogged.
This is also particularly true of typical house dust which is distinguished by a considerable portion of fibres. The filter cake forming on the sieve-plate facing the incoming flow would make any further operating impossible after only a very short time.
What is also disadvantageous is that in this arrangement only very large spheres with a corresponding small surface and correspondingly small binding capacity for fine dust can be used. Smaller spheres would have to be held back using even finer sieves in the upstream filter, which leads to even greater problems with coarse/fibre-containing dust.